1. Field of the Invention
The present invention relates to a plate roofing material referred to as, for example, artificial slate which is superior in waterproofing properties, good design and handling properties and is made of a cement material.
As the plate roofing material, various ones have been conventionally used. Very important to the roofing material are as follows: First, no leaks in a roof covered with roofing materials are very important. Second, the harmony with a building is very important. That is, the good design of roofing materials, to say nothing of a building roofed over with the roofing materials, is very important in terms of the sight from the streets and the houses. Third, it is important that roofing materials are not easily damaged and are superior in handling properties and workability when the roofing materials are transported from a factory to a construction field and a building is roofed over with the roofing materials in the construction field.
2. Description of the Prior Art
A roofing material raises very important problems in terms of any of the function, the good design, and the handling properties as described above. The good design becomes a more important factor as houses have been recently constructed higher in grade.
As one example of the roofing material, clayslate which is a kind of clay stone has been conventionally well-known as a high-grade natural slate roofing tile. In the roofing work, a roof is covered with roofing materials divided into pieces in a staggered manner such that their jointing lines in the longitudinal direction are not overlapped with each other. Consequently, a massive roof is completed, which is a problem in terms of the workability.
In recent years, the demand for an artificial roofing material superior in workability which is very similar in appearance to natural slate such as clayslate has been increased as houses have been constructed higher in grade. Therefore, a large-sized artificial plate roofing material referred to as, for example, artificial slate made of a cement material to imitate the appearance of natural slate has been proposed. In order that the jointing line in the longitudinal direction of each of the roofing materials is not noticeable and such an appearance is presented that the surface of a roof is covered with a lot of natural slate roofing materials divided into pieces as described above, however, at least one longitudinal groove is formed on the surface of an exposure portion of the roofing material.
In the case of rain with a strong wind such as a typhoon, however, rainwater on the surface of the roofing material is pushed up along the above longitudinal groove by wind pressure, to easily enter an overlapped portion of the roofing material, which causes leaks in the roof. At the present time, therefore, the longitudinal groove is a shallow and narrow one in which rainwater is not easily accumulated. As a result, the surface of the roof lacks a three-dimensional feeling and the design thereof becomes monotonous, so that the present artificial plate roofing material cannot give the surface of the roof a high grade.
On the other hand, as in the invention described in Japanese Utility Model Laid-Open Gazette No. 117411/1976, a roofing material having a groove folded down the middle so that rainwater is not easily pushed up by the wind has been proposed. However, rainwater does not easily flow down in the groove. Consequently, rainwater remains on the surface of a roof so that dust easily adheres thereto, which causes the growth of moss in a long time, spoiling the beauty of the building.
Furthermore, in an artificial plate roofing material which imitates natural slate, a pattern is made out of the surface of natural slate, and a thin and large-sized cement plate roofing material is artificially formed utilizing the pattern. Since a pattern is made out of natural slate, however, the surface of the roofing material is of a rugged pattern which is irregular in height. When a roof is covered with roofing materials, therefore, if a worker walks on a roofing material during the work, the weight of the worker is concentrated on the highest part of the overlapped portion of the roofing material, so that the roofing material is stepped on and broken depending on how the overlapped roofing materials are brought into contact with each other.
Additionally, also when the roofing materials are transported when they are overlapped with each other, the roofing materials are inclined and shaky so that they are easily broken because the overlapped surfaces are not fixed for the same reason.